Tissue cultured bovine endothelial cells (EC) are being subjected to flow conditions in an in vitro circulatory loop. The cells are cultured on different biomaterial and conventional substrates in a stationary environment, then transferred to the flow loop for up to 2 weeks. Complete tissue culture medium is circulated by a pulsatile pump to simulate the flow and pressure in the descending thoracic aorta. Thus far the response of the cells to flow has been enlargement and proliferation on the microfabric substrate, compared to controls maintained in stationary culture. During the coming year the response of cells cultured on dacron knit backed with Silastic will be studied, and attempts to culture human saphenous vein endothelial cells will be continued. Furhtermore the fluid mechanical properties of the loop will be changed to obtain different flow velocity profiles.